Chapter 2 Section 2 Newton’s Laws of Motion · Chapter menu Resources Newton’s First Law of Motion An object at rest remains at rest, and an object in motion remains in motion

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Section 2 Newton’s Laws of Motion

Bellwork

If you are sitting still in your seat on a bus that is

traveling 100 km/h on a highway, is your body at rest

or in motion? Explain your answer. Use a diagram if it

will help make your answer clear.

Chapter 2



Newton’s First Law of Motion

An object at rest remains at rest, and an object in

motion remains in motion at a constant speed and in a

straight line unless acted on by an unbalanced force.

• Newton’s first law of motion describes the motion of

an object that has a net force of 0 N acting on it.

Chapter 2 Section 2 Newton’s Laws of Motion



Newton’s First Law of Motion, continued

• Part 1: Objects at Rest Objects at rest will stay at

rest unless they are acted on by an unbalanced force.

• Part 2: Objects in Motion Objects will continue to

move with the same velocity unless an unbalanced

force acts on them.

• The image on the next slide shows how you can have

fun with Newton’s first law.




Newton’s First Law of Motion, continued





• Friction and Newton’s First Law Friction between

an object and the surface it is moving over is an

example of an unbalanced force that stops motion.

• Inertia and Newton’s First Law Newton’s first law

is sometimes called the law of inertia. Inertia is the

tendency of all objects to resist any change in motion.



• Mass and Inertia Mass is a measure of inertia. An

object that has a small mass has less inertia than an

object that has a large mass.

• So, changing the motion of an object that has a small

mass is easier than changing the motion of an object

that has a large mass.




Newton’s Second Law of Motion

The acceleration of an object depends on the mass of

the object and the amount of force applied.

• Newton’s second law describes the motion of an

object when an unbalanced force acts on the object.




• Part 1: Acceleration Depends on Mass The

acceleration of an object decreases as its mass

increases. Its acceleration increases as its mass

decreases.

• Part 2: Acceleration Depends on Force An object’s

acceleration increases as the force on the object

increases. The acceleration of an object is always in

the same direction as the force applied.







Chapter 2

• Expressing Newton’s Second Law Mathematically

The relationship of acceleration (a) to mass (m) and

force (F) can be expressed mathematically with the

following equation:

Section 2 Newton’s Laws of Motion

m a = F

m , or F = a



Newton’s Third Law of Motion


Whenever one object exerts a force on a second

object, the second object exerts an equal and opposite

force on the first.

• Newton’s third law of motion can be simply stated as

follows: All forces act in pairs.




• Force Pairs Do Not Act on the Same Object A

force is always exerted by one object on another

object. This rule is true for all forces, including action

and reaction forces.

• Action and reaction forces in a pair do not act on the

same object. If they did, the net force would always be

0 N and nothing would ever move!



• All Forces Act in Pairs—Action and Reaction

Newton’s third law says that all forces act in pairs.

When a force is exerted, there is always a reaction

force.




• The Effect of a Reaction Can Be Difficult to See

When an object falls, gravity pulls the object toward

Earth and pulls Earth toward the object.

• You don’t notice Earth being pulled upward because

the mass of Earth is much larger than the mass of the

object. Thus, the acceleration of Earth is much smaller

than the acceleration of the object.




2. During a laboratory

experiment, liquid was

collected in a graduated

cylinder. What is the

volume of the liquid?

F 30 mL

G 35 mL

H 40 mL

I 45 mL

Chapter 6 Standardized Test Preparation

























Chapter 2 Section 2 Newton’s Laws of Motion · Chapter menu Resources Newton’s First Law of Motion An object at rest remains at rest, and an object in motion remains in motion

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